How this system works? ... Rly i don't understand..

People having on cata like: 69 - 20 win/loss ration have less more arena mmr/rating than R1/R2 team having.

MMR/Rating system broken or its complete garbage? .. I never saw in my entire life this stupid system its feels like you lost 30 games and after won 30 you be like 2.4k rated how come?...